Cloud Computing and the Rise of Silicon Photonics

The business of today’s data-driven world is being conducted in the Cloud. The rapid growth of cloud computing requires data centers to dramatically scale up in order to handle the oceans of data that must be transferred between systems quickly and without congestion. As this growth continues, traditional copper presents limitations in distance, bandwidth, and efficiency for IT planners. Devices based on silicon photonics technology are poised to revolutionize data efficiency because they use laser light to transfer data from chip to chip, which is much faster and can achieve higher data rates and greater distance than switching via electrical connections over copper cabling.

Silicon photonics technology has captured the industry’s attention because the devices use the CMOS fabrication process that is common with semiconductor chips, whereby sophisticated photonic devices can be printed or etched on a chip and then mass-produced on silicon wafers. Thus, they can be produced very fast and without the costs associated with hand-assembling the transceiver.

Very High Integration, Dramatic Performance Benefits

Using just a single connector and single fiber, silicon photonics allows wave division multiplexing (WDM) to bring a very high level of integration and dramatic performance benefits to rack equipment. Aggregating serial optical lanes means that equipment vendors can achieve speeds up to 100Gb/s to eliminate I/O congestion. Silicon photonic devices also have a very small form factor to enable higher port density. This past May, for example, researchers at IBM tested a fully integrated wavelength multiplexed silicon photonics chip, which uses four different colors of light traveling with an optical fiber. Within one second, according to the company, “it can share six million images, and it can download an entire high-definition movie within two seconds. The technology allows for the integration of various optical components side by side on a single chip.”

“Normally, you would have specialized structures that were multiplexing and demultiplexing the different colors,” said Kevin Deierling, vice president of marketing at Mellanox, which provides end-to-end connectivity solutions for the data center. “On our silicon photonics platform, we’ll take multiple modulators and then combine and multiplex the different wavelengths of light together and send it out on a single fiber, and on the receive side we’ll demux the different colors, by literally building a sort of prism into the silicon photonics substrate.” This level of integration, along with the promise of higher volumes, will help data center equipment vendors lower their costs.

A 100Gb/s silicon photonics active optical cable from Mellanox

Since silicon-photonics-based data transmission aims to free servers of the copper cables that connect them, airflow within the racks improves because of their absence. Cooling servers can be a significant expense, so fewer copper cables mean that data center managers can reduce costs substantially by selecting silicon-photonics-based equipment.

Another potential benefit is rack disaggregation. In a typical server rack, all of the modules housed within it have a separate function (such as networking, power, storage, compute). According to Tom Simonite, in an article in the MIT Technology Review, in a few years, the higher bandwidth that silicon-photonics-based connections provide can transform the server rack to one in which modules that address each function can be grouped together for more efficient upgrading and more targeted cooling.

Disaggregate the Rack

Intel had the disaggregated rack in mind last year when it announced a partnership with Corning, Molex, Tyco Electronics, and US Conec to develop MXC optical cables capable of delivering data at 800Gb/s up to 300 meters in each direction. The cables promise to be smaller and more bendable than copper for deployment in tight spaces. MXC interface technology uses micro lenses to provide very high density and exceptional functionality and reliability for data center environments.

An MXC connector from Molex

“MXC interfaces offer a density improvement of 40% over traditional MPO/MTP interconnects,” said Tom Marrapode, director of advanced technology development for Molex Optical Solutions, which offers a wide range of connectivity solutions for telecom, data center, military, and medical markets. “MXC is easier to use mechanically due to the incorporation of an RJ-style latch versus MPOs’ push-pull latching. Higher front panel densities can be achieved.” The company’s MXC cable assemblies with 12 to 48 multimode OM3 or OM4 fibers are available with receptacles that mount into panel cutouts, and internal ribbon fiber assemblies connecting to active devices.

Who Will Migrate First?

Widespread adoption of silicon photonics technology will not happen overnight. In many cases, it simply is not realistic for a data center manager to disrupt operations and replace all the equipment for bleeding-edge fiber and cable. Further, this past February, Intel announced it would delay shipments of its silicon photonics modules and in turn, the cables will not be installed in servers before the end of the year. The earliest adopters of silicon photonics technology will be the enterprises that have both the greatest data-intensive systems and the resources to scale up their facilities all at once. For most enterprises, however, the migration to silicon photonics will be gradual.

Expect copper, multimode VCSEL-based laser technology, and silicon-photonics-based devices to coexist in the market for a few more years. During that time, connector vendors will continue to offer industry standard QSFP and SFP form factors for customers that want the flexibility to migrate from 10Gb/s and 40Gb/s solutions to speeds that reach 100Gb/s as their needs, economics, and multiplexing technologies make sense.

According to Kevin Deierling of Mellanox, the beauty of silicon photonics is that “you can lay down some single-mode fiber plants and know that you can go higher speed modulation, you can go WDM, then you can just keep driving more and more data through the same pipes that you already laid.”

The Sky’s the Limit

Whether enterprises scale up all at once or take a more gradual approach, silicon photonics technology will drive the data center’s future. Higher bandwidths, less cabling, and better reach will ensure that companies can scale up their cloud computing infrastructures flexibly and economically to meet society’s ever-increasing demands for big data.

Author Chris Warner is a freelance technology writer who comes from an old Western Electric family. He has more than 15 years experience in covering the electronic components industry.